The overall objective is to study the function of dog heart, liver, small intestine and skeletal muscle lymph vessels in edema. Lymph vessels normally function to remove excess fluid from the tissues and edema can develop only when the lymph vessels are unable to remove fluid as fast as it filters into the tissues. In edema lymph flow may increase either because there is an increased pressure driving lymph from the tissues or because lymph vessel resistance is decreased. The relative contributions of these two mechanisms determines the lymphatic response to edema in a given tissue. For instance if the pressure driving lymph from a tissue is low, then the lymph vessel may not be able to transport lymph against an elevated venous pressure. Venous pressure is frequently elevated in critically ill patients. The first specific aim is to evaluate the contributions of driving pressure and lymph vessel resistance to the lymph flow response to edema in each tissue. The driving pressure and resistance will be calculated from the relationship between lymph flow and lymph vessel outflow pressure. The second specific aim is to evaluate the role of elevated venous pressure in opposing lymph flow and promoting edema. This will involve elevating the superior vena caval pressure (the pressure into which lymph vessels must flow) and estimating the amount of edema in the tissues. The third specific aim will involve estimating the effects of motion of the tissues around lymph vessels on the pressure of the lymphatic pump. This will be accomplished by measuring the lymph driving pressure in the skeletal muscle lymph vessels as skeletal muscle contraction rate is varied. These studies should increase our knowledge of the role of the lymphatic system in preventing edema in various tissues of critically ill patients.